The recent Mediterranean fruit fly incident illustrated a problem that exists in this country--the possibility of shipping infested fruit throughout the country and causing colonies of fruit flies to appear in uninfested areas. The Mediterranean fruit fly is one of a number of fruit flies which can infest different kinds of fruit.
The life cycle is the same for each type of fly. The female fruit fly has an ovipositor at the end of its abdomen which is inserted into a host fruit. Barbs at the base of the ovipositor hold the ovipositor to the fruit surface while the eggs are laid within the fruit. The eggs hatch within the fruit and the larva use the fruit as a food supply. The adult flies emerge from the fruit, mate and new eggs are laid within the new host fruit. If the fruit has been transported from one location to another, then the fruit flies will emerge and propagate in the new location if suitable host fruit can be found.
This is presumably what happened in the recent Mediterranean fruit fly incident in which it was thought that a host fruit was carried from Hawaii to California. There the adult fruit flies emerged and found new and different host fruit in which to lay eggs. A concern was that the cycle would repeat itself throughout the country.
The fruit flies will lay eggs both in fruit on the tree and in picked fruit in containers, if they have access to the latter fruit. For this reason, the fruit is normally packed in fully enclosed containers, such as a fully enclosed regular slotted container or fully enclosed telescopic half slotted container or fully enclosed containers of the types shown in Du Barry U.S. Pat. No. 3,434,648 granted Mar. 25, 1969 and Chaffers U.S. Pat. No. 3,946,934 granted Mar. 30, 1976. Another type of fully enclosed container, a large tray which has a telescoping cover is shown in Putnam U.S. Pat. No. 3,940,053 granted Feb. 24, 1976.
It would be preferrable to have a container with adequate ventilation to prevent premature ripening, to improve ventilation and cooling, and to allow for the escape of the ethylene gas produced by the fruit. Many fruits, such as avocados, must be ventilated during shipment and storage. Such a ventilated container is shown in Chaffers U.S. Pat. No. 3,713,579 granted Jan. 30, 1973. Unfortunately, the ventilation holes will allow the fruit fly to lay eggs within the fruit.
The Putman and Chaffers patents also disclose corrugated containers with laminated walls.
The ovipositor is not a single element. It has three elements or sections. These are shown diagramatically in FIG. 7. In this figure the ovipositor is shown in its extended position. The segment VII is next to the abdomen D. It houses segment VIII and pat of segment IX, and has barbs on its outer face for holding the ovipositor in the fruit. Segment VIII is a membraneous telescoping sheath which has chitinous slides or guides which slide telescopically into and out of segment VII. This action is hydraulic using the body fluids of the fly and a pumping action to pump the guides and segment IX into the fruit. If segment IX extends further than segment VIII allows, then segment IX is without support and the ovipositor is useless.
The eggs are deposited from the outer tip segment IX but segment VIII must penetrate the fruit if this is to happen.
The ovipositor shown in FIG. 7 is not to scale. The length of ovipositors of flies have been measured by D. E. Hardy. His 1974 monograph "The Fruit Flies of the Philippines" Pacific Insects Monograph 32:1-266, Bernice P. Bishop Museum, Honolulu, Hawaii lists the mean length and standard deviation of the ovipositor and its individual segments. These are based on the measurements of 100 ovipositors for each of three species of laboratory reared fruit flies, and for wild fruit flies. These are given in Table I.
TABLE I __________________________________________________________________________ Laboratory Wild VII VIII IX OP VII VIII IX OP Species ML SD ML SD ML SD ML SD ML ML ML ML __________________________________________________________________________ C. capitata 1.0 0.07 1.1 0.10 1.1 0.05 3.2 0.12 -- -- -- -- D. cucurbitae 1.5 0.10 2.6 0.14 1.6 0.06 5.6 0.20 1.5 1.9 1.6 5.0 D. dorsalis 1.1 0.05 1.9 0.14 1.5 0.12 4.5 0.12 1.2 1.6 1.5 4.3 __________________________________________________________________________ Laboratory = Laboratoryreared flies Wild = Wild flies VII = Segment VII VIII = Segment VIII IX = Segment IX OP = Ovipositor ML = Mean length, mm SD = Standard deviation, mm
The longest ovipositor is that of the melon fly which has a length of 5.8 mm and a standard deviation of 0.20 mm.
A study by the Hawaiian Fruit Flies Laboratory in 1978 indicated that the penetration of the fruit by the ovipositor will depend upon the ripeness or maturity of the fruit. The fly has more difficulty penetrating an unripe or harvest mature fruit than penetrating a ripe fruit. An experiment was performed using Brazilian bananas. The mean depth of puncture was for C. capitata 1.9 mm in unripe bananas and 2.4 mm in ripe bananas; for D. cucurbitae 3.3 mm in unripe bananas and 5.2 mm in ripe bananas; and for D. dorsalis 2.1 mm in unripe bananas and 3.5 mm in ripe bananas.